The Easiest Way to Build your First iPhone App | Nettuts+

PhoneGap is an open-source framework that can turn any web app into a native app for iPhone, BlackBerry and Android. It pulls off this trick by running your web code in a UIWebView, an embedded instance of Safari without the toolbars and buttons of the standalone Safari app. PhoneGap then extends this basic functionality by mapping features of the iPhone SDK to JavaScript objects you can call in your web code, so you can easily add features like GPS, camera, contacts, vibration, SQLLite and accelerometer support. And when you’re ready to distribute your app, PhoneGap 0.80 is Apple-approved!
(Link: The Easiest Way to Build your First iPhone App | Nettuts+)